The present invention, generally, relates to storage systems, more particularly, to methods and/or systems for copying from source media to target media in storage systems.
Hierarchical storage systems integrating with a tape storage system, in which a part of files is stored on tape media, have been developed. In the hierarchical storage systems, there may be provided a hierarchical storage management (HSM) functionality that performs several operations such as migration and recall between storage tiers. The HSM may move the file's data on a disk tier to back-end tape tier. When users or programs access the file, the HSM may automatically recall the file's data from the back-end tape tier.
One of the operations provided by the HSM in the hierarchical storage systems is reclamation, in which merely active data on a source medium is copied to another target medium so as to defragment active data on the medium. The reclamation process can be performed so that all active data stored on the source medium with low usage are moved to another tape medium in order to improve overall tape usage. For example, a particular implementation may automatically trigger the reclamation process when the ratio of the active data on the tape medium falls below a predetermined level (e.g. 35%).
Data may be scattered over the tape medium due to modification or deletion of files. Since tape drives may take some time to locate start position of each active data on the source medium due to their sequential nature, a reading time associated with reading a series of data (e.g., which may constitute a single file, a group of files, etc.) may be prolonged. Even though two drives are occupied during the reclamation process, the drive for the target medium may not always operate; there is a waiting time for the data to be transferred from the source medium, meaning that the drive resources are not fully utilized.
Such inefficiencies may also arise in inter-generation copies (or inter-generation migrations), in which data on an old generation tape medium is copied to a new generation tape medium. Typically, transfer rate for a new generation is higher than those for old generations. In this case, the write transfer rate for the new-generation medium may be adapted to the read transfer rate for the older-generation by a speed matching capability of the tape drives. Hence, the drive resources during the inter-generation copy are also not fully utilized.
Since the plurality of the drives are occupied during copy processes between media such as reclamation and inter-generation copy, other operations, e.g., such as migration and recall may be prevented: However, there exists a waiting time during which the capability of the drive is not effectively utilized.
In sharp contrast, methods, computer systems, storage systems and/or computer program products described in some of the various embodiments herein may be capable of effectively utilizing a waiting time during which the capability of the drive is not utilized for writing data transferred from a source medium to a target medium in a storage system, as will be described in further detail below.